1. Field of the Invention
The present invention relates to a fuel injection valve.
2. Description of the Related Art
Japanese Unexamined Patent Publication No. 2000-257534 discloses a fuel injection valve for injecting fuel into the combustion chamber of the internal combustion engine. This fuel injection valve comprises a fuel injection port (referred to, in the publication cited above, as “the fuel injection holes” designated by reference numeral 8) and a member for closing the fuel injection port (in the cited publication, corresponds to a movable portion 4A including a plunger 4, a rod 5 and a valve body 6, and hereinafter referred to as “the movable portion” as in the cited publication). In this fuel injection valve, the movable portion is subjected to the force generated by the fuel pressure (hereinafter referred to as “the valve opening force due to the fuel pressure”) acting on the movable portion in the direction to open the fuel injection port (hereinafter referred to as “the valve opening direction”), the force generated by the fuel pressure (hereinafter referred to as “the valve closing force due to the fuel pressure”) acting on the movable portion in the direction to close the fuel injection port (hereinafter referred to as “the valve closing direction”) and the force generated by a spring (hereinafter referred to as “the valve closing force due to the spring”) acting on the movable portion in the valve closing direction. Also, this fuel injection valve includes a means (hereinafter referred to as “the electromagnetic means”) for electromagnetically generating the force acting on the movable portion in the valve opening direction.
In the fuel injection valve disclosed in the publication cited above, as the sum of the two valve closing forces (i.e. the valve closing forces due to the fuel pressure and the spring) is larger than the valve opening force due to the fuel pressure, the fuel injection port is closed by the movable portion in the case where the force from the electromagnetic means (hereinafter referred to as “the valve opening force due to the electromagnetic means”) is not generated. In view of the fact that the total valve opening force due to the electromagnetic means and the fuel pressure is larger than the total valve closing force due to the fuel pressure and the spring, on the other hand, the movable portion is moved away from the fuel injection port thereby to open the fuel injection port and inject the fuel from the fuel injection port when the force is generated by the electromagnetic means.
In the fuel injection valve disclosed in the cited publication, when the force is generated by the electromagnetic means and the movable portion is moved away from the fuel injection port, the valve opening force due to the fuel pressure increases with the distance covered by the movable portion. When the movable portion is moved to the point farthest from the fuel injection port, the valve opening force due to the fuel pressure assumes a maximum value substantially equal to the valve closing force due to the fuel pressure. In the case where the valve opening force due to the electromagnetic means ceases to be generated under this condition, the movable portion closes the fuel injection port. As the valve opening force due to the fuel pressure is substantially equal to the valve closing force due to the fuel pressure under this condition, as described above, the overall valve closing force cannot be increased by controlling the fuel pressure. In order to cause the movable portion to close the fuel injection port satisfactorily, therefore, the valve closing force due to the spring is required to be correspondingly large.
The valve opening force due to the fuel pressure is small when the fuel injection port is closed by the movable portion. In order to cause the movable portion to move satisfactorily in the case where the valve closing force due to the spring is excessively large, therefore, it is necessary to use an electromagnetic means of high performance (i.e. an electromagnetic means capable of generating a larger valve opening force). Generally, the electromagnetic means of high performance is large in size. In the case where the electromagnetic means of high performance is required, therefore, the use of an electromagnetic means large in size is unavoidable, thereby leading to a large fuel injection valve. In the case where the fuel injection valve is mounted on the internal combustion engine, for example, the mountability of the fuel injection valve on the internal combustion engine is deteriorated. Also, a bulky electromagnetic means is generally low in responsiveness.
Accordingly, the object of this invention is to provide a fuel injection valve requiring no large electromagnetic means (generally, no electromagnetic means of high performance).